A REPORT exploring the financial implications of burying power lines underground shows that energy bosses have “grossly exaggerated” the costs, campaigners from Suffolk and Essex said last night.

An independent inquiry into the comparative costs of overground and underground high power cables, commissioned by the Department for Climate Change in 2010, was published yesterday.

The National Grid has previously ruled out an underground route for the 400,000 volt power lines that it is looking to install alongside its existing cables from Bramford, near Ipswich, to Twinstead, near Sudbury.

It has said burying cable, which would carry power from Sizewell C and offshore wind farms, through some of the area’s most beautiful countryside, would mean a cost up to 17 times that of pylons.

But yesterday’s report shows that the difference in cost between putting cables underground compared to overhead is not so large.

Overhead power lines are the cheapest option – with a lifetime cost varying between �2.2m and �4.2m per km, according to the report.

The cheapest undergrounding option is direct burial, with a varying lifetime cost of between �10.2m and �24.1m per km – around five times the cost of overhead pylons.

A gas-insulated line, which is favoured by campaigners, would have a lifetime cost of between �13.1m and �16.2m per km. However the report adds such technology should be kept “under review”.

Last night David Holland, chairman of campaign group Stour Valley Underground, which claims giant pylons would ruin swathes of countryside, said the report showed installing gas-insulated line technology was “entirely possible”.

“The report is a valuable piece of documentation and clearly shows National Grid has vastly exaggerated the cost of underground transmission,” Mr Holland said.

“However, one of the big problems as far as we are concerned is that it does not look at the social and environmental costs. It looks at the costs purely from the point of the energy industry. There are other issues as well, such as the effect overhead power lines would have on a historically important landscape and the impact they could have on the tourism industry, vitally important to the economies of both Suffolk and Essex.”

South Suffolk MP Tim Yeo said: “We have heard consistently alarming estimates about how much extra it would be to underground electricity cables. From the report it is clear that the costs are nowhere near as high as National Grid has been quoting.

“What we can now calculate is how much extra that would put on our bills.

“It may be around �3 or �4, which I think is perfectly acceptable to protect our wonderful landscape and would offer assurance to not just people in Suffolk but people everywhere who are fighting similar proposals.”

A spokeswoman for National Grid said: “The costs of different technology options contained in the report are broadly in line with those that National Grid have used and published when carrying out appraisal of options on current projects such as Bramford to Twinstead and Hinkley Point. This is true whether using capital cost or lifetime cost.

“National Grid will take time to digest the detail contained in the report and if there is any new information we need to take into account in any of our current plans, or changes to the way in which we evaluate project options going forwards, then of course we will do so.”